A combination of a magnetic structure and a magnetic field sensor forms a contactless position encoder with which linear relative motions can be measured. Position encoders for paths in the millimeter range are currently used in large numbers in apparatuses of machine and car industry.
In the case of applications in which the position encoders are subject to high levels of dirt such as dust, fibers, oil vapors, etc., magnetic position encoders represent a sturdy and cheap alternative to the widely used optical position encoders because they do not require any tight encapsulation between the moved and the unmoved mechanical part of the apparatus.
A combination of a magnetic structure and a magnetic field sensor can also form an angle encoder with which a rotational angle can be measured.
A method for contactless determination of linear relative motions between a magnetic structure and electronic sensors is known from EP 979988. The magnetic structure contains either a single axially magnetized permanent magnet or several permanent magnets which are arranged next to one another and are magnetized in a helical manner. The sensors are arranged laterally spaced from the permanent magnets and measure the radial and axial component of the magnetic field generated by the magnetic structure.
From EP 1243897 an apparatus is known in which the magnetic field generated by the magnetic structure is rotationally symmetrical with respect to an axis of symmetry and a magnetic field sensor measures two components of the magnetic field which are situated in a plane extending orthogonally to the axis of symmetry of the magnetic field source.